The Heat Production of the Albino Rat

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Abstract
A closed-circuit respiration chamber for measuring (usually in 2-hour periods) both the carbon-dioxide production and the oxygen consumption of the rat is described, and the methods employed by other investigators in studying the gaseous metabolism of the rat are listed. Description of the method of graphic registration of the rat's activity and discussion of the quantitative interpretation of such records is followed by a study of the relation between the rat's metabolism and its activity. It is concluded that the ideal experiments are those with complete muscular repose, that in 2-hour periods a minor amount of muscular activity is in general without effect upon the metabolism, that momentary excessive activity has only a minor influence in a 2-hour period, and that repeated, intermittent activity, if not long continued, causes an increase in metabolism of not over 15 to 20 per cent. The necessity for graphic registration of activity as an index of whether the conditions of repose have been ideal for basal metabolism measurements has therefore been over-emphasized in the case of the rat. In general, ocular observation of the activity and discarding of results obtained when the rat is seen to be constantly moving (especially during the study of the influence of a subtle, superimposed factor) will be sufficient. The heat production of rats over 4 1/2 months old (reported as large calories per square meter of body surface per 24 hours), measured at 26° C., decreased on the average from 7 to 13 per cent during the first 17 to 24 hours without food, but remained essentially constant thereafter up to the sixty-fourth hour. The effect of any superimposed factor can thus be satisfactorily studied after the rat has been fasting 17 hours. With rats younger than 4 months the metabolism decreased 28 per cent during the first 24 hours of fasting. The younger organism is therefore not so well able to withstand fasting.1